The loss of biodiversity is one of the most pressing environmental issues. However, in the protection of biodiversity, short-term particular interests often prevail over long-term general interests. This is different in the Lower Oder Valley National Park, in the state of Brandenburg: here, non-state actors have been able to shift the balance of power in their favor. The diverse activities of the Friends of the German-Polish Europe National Park Lower Oder Valley association have opened up new avenues for action. However, the political impact of this third-sector organization can only be understood by considering additional factors: the transformation process of the former GDR significantly influenced the establishment of the national park. Furthermore, the specific policy arrangement has set essential parameters for environmental policy advocacy.